1. Field of the Invention
The present invention relates to a method and device for quantitatively determining an analyte that is used for biochips, DNA chips, etc. as well as a method for attaching molecules to a substrate that is used for biochips, DNA chips, etc., and a device manufactured using the method.
2. Description of the Related Art
Recently nanotechnology has become a key word which has drawn much attention from many people, caused by various factors including a nanotechnology initiative proposed in United States in 2,000. Specifically, the nano-biotechnology field that is an integration of semiconductor microprocessing technologies (semiconductor nanotechnologies) and biotechnologies is expected as a new technical field that may bring about drastic solutions to the conventional problems, and many researchers are working energetically in this field.
Among these, the biochip technologies represented by DNA chips (or DNA microarrays) attract attention as an effective means for gene analysis. Biochips comprise substrates made of glasses, silicon, plastics, etc. on the surface of which numerous different test substances of biomacromolecules such as DNAs and proteins, are highly densely arrayed as spots. They can simplify examination of nucleic acids and proteins in the fields of clinical diagnosis and pharmacotherapy (see, for example, Japanese Unexamined Patent Application Publication No. 2001-235468 (paragraph numbers 0002–0009), and Annual Review of Biomedical Engineering, vol. 4, p. 129–153, 2002, and Nature Biotechnology, vol. 21, p. 1192–1199, 2003).
Devices, such as those chips, manufactured by integrating micromachining technologies and sensing technologies under technologies for detecting a tiny analyte, are generally called MEMSs or μTASs, which draw attention as devices for greatly improving the detection sensitivity and detection time compared with the prior art. The term MEMS is the abbreviation of Micro Electro Mechanical System, that is, a technology to prepare microscopic matters, based on semiconductor processing technologies, or microscopic, precision devices prepared, using the technologies. In general, it is a system wherein a plurality of functional units such as mechanical, optical and hydrodynamic units are integrated and miniaturized. The term μ-TAS is an abbreviation of Micro Total Analysis System, and is a chemical analysis system with micropumps, microvalves, sensors or the like, miniaturized, accumulated, and integrated.
The features of these devices are that it is possible to evaluate a very small amount of a sample containing an analyte, and that it is possible to perform a real-time evaluation by making a sample flow into an analyte detecting unit. There are many other advantages including one that it is possible to evaluate a plurality of analytes at the same time, by arranging analyte detecting units in parallel or in series.
Furthermore, regarding the technology that is a key for these nano-biotechnologies, there is an issue how biomolecules such as DNAs and proteins should be attached to a solid such as a semiconducting material and metal, in order to make the surface of the solid have a specific function. Attaching of molecules to the surface of a solid by physical adsorption represented by LB (Langmuir Brodgett) membranes have been long and widely known. However, the molecules formed only by physical adsorption are stripped off as time passes, or by repetitive use. Accordingly, attachment of molecules by chemical adsorption utilizing a chemical reaction between the surface of a solid and molecules has been generally used recently. Specifically, a method for attaching molecules by chemical adsorption wherein an SH (thiol) group is placed at an end of a molecule to utilize covalent bonding between S (sulfur) and a metal or semiconducting material, is proposed, and is widely used in various researches and developments (see, for example, Chemical Reviews, vol. 96, p. 1533–1554, 1996).
When molecules having an alkyl chain which has an SH end group is used as the molecules, a monomolecular film with a regular array of molecules can be formed on a solid, by means of van der Waals force of the alkyl chain. It is easy to form this membrane. That is, when the surface of a solid is immersed in a solution containing these molecules, a monomolecular film (self-assembled monolayer film) is spontaneously formed on the surface of the solid.
It is possible to form a monolayer film having a function on the surface, by attaching DNAs, proteins, or functional groups having other functions to a part of the alkyl chain (see, for example, Bioconjugate Chemistry, vol. 8, p. 31–37, 1997).